1. Field of the Invention
The present invention relates to a structure for attaching wire guides which guide operation wires incorporated in the insertion section of an endoscope and, more particularly, to an endoscope provided with an improved structure for attaching the wire guides.
2. Description of the Related Art
A typical endoscope includes an operating section, an insertion section which is inserted into a cavity of the human body, a light guide cable connected to the operating section, and a light source connector section for connecting the light guide cable to an illuminating light source means.
Wires for causing the foremost end portion of the insertion section to bend and wire guides for guiding these wires are arranged inside the insertion section of the endoscope. A typical wire guide attaching structure is disclosed in, for example, Japanese Patent Disclosure (Koki) No. 59-69024.
The process of assembling the insertion section of a typical endoscope will now be described, with reference to FIGS. 1 through 3. As is shown in FIG. 1, the insertion section is made up of three separate units which are subsequently assembled into a single piece. First unit L has a housing which forms the distal end of the insertion section and to which are attached image and light guide fibers, an objective lens system, operating wires and so forth. Cap member L1, mounted on the base end portion of the light guide fiber handle of first unit L, is inserted into second unit M (or bending tube having wire guide rings M1), followed by the body of first unit L. In addition, cap member L1 of first unit L is inserted into third unit N (or flexible tube portion), again followed by the body of first unit L. Finally, the first, second, and third units are joined together, being secured to one another by means of a bonding agent or the like.
When the above-described assembly process has been completed, coating tube L2 is attached round cap member L1. Diameter A which is obtained by adding the thickness of coating tube L2 to the outer diameter of cap member L1 must be made smaller than the inner diameter of the guide ring portion of the bending tube. In addition, it must be made smaller than the smallest inner diameter C at coupling tube N1 where the bending and flexible tubes of the insertion section are connected to each other, particularly at that portion of the insertion section to which wire guides N2 are attached in FIG. 3. Therefore, the cap member must be smaller than the smallest inner diameter of the insertion section of the endoscope.
Cap member L1 is hard and cannot be deformed in its radial direction, but the other portion of the internal matters which is coated by coating tube L2 is soft and can be deformed in its radial direction. If the hard portion of first unit L which has diameter A can be inserted into second and third units, the insertion section can be assembled. Therefore, that portion of third unit N which has the smallest diameter C, as shown in FIG. 3, is important. As shown in FIG. 2, the foremost end of the wire guides are fitted into cut-away slits in coupling tube N1 at that portion of third unit N and fixed there by filling a bonding agent in the slit.
When the insertion section of the endoscope which is assembled according to the above-described process is to be made still smaller in its outer diameter, the wire guides must be made still slimmer. However, they need to have such a strength that they cannot be deformed by the pulling force of the operating wire, and they must be made thick to some extent accordingly. Therefore, there is a limit in making them slimmer.
This asks that the wire guide attaching structure is improved in order to make the insertion section of the endoscope smaller in its outer diameter.